From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Dmitry Safonov <0x7f454c46@gmail.com>,
khorenko@virtuozzo.com,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Cyrill Gorcunov <gorcunov@openvz.org>,
xemul@virtuozzo.com, X86 ML <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)
Date: Mon, 13 Jun 2016 15:50:20 +0200 [thread overview]
Message-ID: <20160613135020.GA27007@redhat.com> (raw)
In-Reply-To: <CALCETrWM1xr_5jkxofdW+iEoTmZpaOFDOBroaaB=UMM1pYct3A@mail.gmail.com>
To avoid the confusion, let me first say that I am not going to argue
with these changes, I simply do not understand the problem space enough.
On 06/10, Andy Lutomirski wrote:
>
> On Fri, Jun 10, 2016 at 1:07 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > IIRC, CRIU can't c/r the 32-bit applications, or this is no longer true?
> >
>
> CRIU has a horrible, nasty, brilliant idea: it will start restoring
> 32-bit processes by treating them mostly like 64-bit processes. The
> restorer will start out 64-bit, set everything up, and long
> jump/return/sigreturn/whatever back to 32-bit mode.
OK, I see,
> My proposal was
> that, rather than coming up with nasty hacks to switch the kernel's
> idea of the task bitness,
Well, I can't resist but to me SA_IA32_ABI/SA_X32_ABI looks like a hack
too. We actually shift TIF_*32 into k_sigaction->flags, and the fact
that we do this per-signal looks, well, interesting ;)
And at first glance it would be very simple to change the task bitness,
CRIU can simply exec a dummy 32-bit application before anything else.
In this case (I think) we also do not need do_map_vdso/ARCH_MAP_VDSO_*
at least right now.
Yes, I guess this will complicate CRIU significantly.
> we instead teach the kernel to respect that
> actual bitness as indicated by CS and the syscalls used to the extent
> possible.
I am still not sure the idea to remove TIF_IA32/TIF_X32 is really good.
But again, I won't argue, I do not feel I understand pro/cons enough.
> So, yes, a restored 32-bit process that crashes should dump core as
> though it's 32-bit even though it was 64-bit when execve was last
> called :)
OK, thanks for you explanation Andy.
Oleg.
next prev parent reply other threads:[~2016-06-13 13:50 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-01 13:11 [PATCH 0/6] x86: 32-bit compatible C/R on x86_64 Dmitry Safonov
2016-06-01 13:11 ` [PATCH 1/6] x86/vdso: unmap vdso blob on vvar mapping failure Dmitry Safonov
2016-06-01 13:11 ` [PATCH 2/6] x86/vdso: introduce do_map_vdso() and vdso_type enum Dmitry Safonov
2016-06-03 9:50 ` Cyrill Gorcunov
2016-06-03 10:03 ` Dmitry Safonov
2016-06-01 13:11 ` [PATCH 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_* Dmitry Safonov
2016-06-01 13:11 ` [PATCH 4/6] x86/coredump: use core regs, rather that TIF_IA32 flag Dmitry Safonov
2016-06-03 9:51 ` Cyrill Gorcunov
2016-06-03 9:56 ` Dmitry Safonov
2016-06-03 10:01 ` Cyrill Gorcunov
2016-06-06 20:45 ` Oleg Nesterov
2016-06-06 22:43 ` Oleg Nesterov
2016-06-08 13:28 ` Dmitry Safonov
2016-06-01 13:11 ` [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Dmitry Safonov
2016-06-03 9:57 ` Cyrill Gorcunov
2016-06-03 10:27 ` Dmitry Safonov
2016-06-03 10:41 ` Cyrill Gorcunov
2016-06-06 21:19 ` Oleg Nesterov
2016-06-07 11:38 ` Dmitry Safonov
2016-06-09 17:21 ` Andy Lutomirski
2016-06-10 20:07 ` Oleg Nesterov
2016-06-10 20:14 ` Andy Lutomirski
2016-06-13 13:50 ` Oleg Nesterov [this message]
2016-06-13 20:40 ` Andy Lutomirski
2016-06-14 14:34 ` Oleg Nesterov
2016-06-14 14:43 ` Dmitry Safonov
2016-06-01 13:11 ` [PATCH 6/6] x86/signal: add SA_{X32,IA32}_ABI sa_flags Dmitry Safonov
2016-06-04 5:08 ` Andy Lutomirski
2016-06-04 15:57 ` Dmitry Safonov
2016-06-01 13:15 ` [PATCH 0/6] x86: 32-bit compatible C/R on x86_64 Dmitry Safonov
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